1. Field of the Invention
The invention relates to implants within body vessels and more particularly to flow diverters, stents and other implants formed of strands of material and having radiopaque properties.
2. Description of the Related Art
Vascular disorders and defects such as aneurysms and other arterio-venous malformations are especially difficult to treat when located near critical tissues or where ready access to a malformation is not available. Both difficulty factors apply especially to cranial aneurysms. Due to the sensitive brain tissue surrounding cranial blood vessels and the restricted access, it is very challenging and often risky to surgically treat defects of the cranial vasculature.
A number of vaso-occlusive devices have been formed of helical windings or coils of metallic wires, braided fibers, and/or woven fibers. Implants formed of non-metallic fibers, or of other materials having a low radiodensity, are difficult to track during insertion through vasculature, placement at a selected site, and possible subsequent recovery. Radiopaque fibers have been added to implants such as described by Engelson et al. in U.S. Pat. No. 5,423,849. However, the diameter of the radiopaque fibers often is very small, typically between 0.0005 to 0.005 inches, and single strands of these fibers are difficult to see during imaging by fluoroscopy or other viewing techniques. Radiopaque materials include platinum, chromium, cobalt, tantalum, tungsten, gold, silver, and alloys thereof.
Depending on the level of radiopacity desired, several techniques are known to increase visibility of an implant during imaging. Additional strands of radiopaque materials are added to the implant, the diameter of the individual strands is increased, and/or the volume of the radiopaque material is increased, such as by forming a coil. However, adding additional strands of radiopaque material may change the mechanical performance of the implant, especially for implants utilizing strands made of shape memory alloy such as Nickel Titanium. Increasing the diameter of the individual radiopaque strands for the implant not only potentially impacts the mechanical performance of the implant but also increases the wall thickness of the implant. Likewise, increasing the volume of radiopaque material by winding the radiopaque filament into a coil and adding it to the implant will impact both the mechanical performance of the implant as well as the thickness of the implant wall.
A composite yarn to reinforce a textile prosthesis is disclosed by Dong in US Patent Publication 2005/0288775. Blood flow diverters which may include braided sections are described by Gobran et al. in US Patent Publication No. 2007/0060994. Stents having radiopaque mesh to serve as filters are presented in U.S. Pat. No. 8,394,119 by Zaver et al. A woven fabric having composite yarns for endoluminal devices is described by Rasmussen et al. in US 2012/0168022.
Another type of vaso-occlusive device is illustrated in U.S. Pat. No. 5,645,558 by Horton as having one or more strands of flexible material which are wound to form a generally spherical or ovoid vaso-occlusive structure when relaxed after being placed in a vascular cavity such as an aneurysm or fistula. Similarly, U.S. Pat. No. 5,916,235 by Guglielmi cites earlier patents describing detachable coils and then discloses an expandable cage as a vaso-occlusive structure that can receive and retain one or more embolic coils after the cage is expanded within an aneurysm. A self-expandable aneurysm filling device is disclosed in US Patent Publication No. 2010/0069948 by Veznedaroglu et al.
Typically, a stent-like vascular reconstruction device is first guided beneath the aneurysm to be treated using a delivery catheter. One commercially available reconstruction product is the CODMAN ENTERPRISE® Vascular Reconstruction Device and System as described, for example, in a Navigate Tough Anatomy brochure Copyright 2009 by Codman & Shurtleff, Inc., 325 Paramount Drive, Raynham, Mass. The CODMAN ENTERPRISE® stent device is carried by a central delivery wire and initially held in place on the delivery wire in a collapsed state by a sheath-type introducer. Typically, a delivery catheter such as a PROWLER® SELECT® Plus microcatheter, also commercially available from Codman & Shurtleff and as disclosed by Gore et al. in U.S. Pat. No. 5,662,622, for example, is first positioned intravascularly with its distal tip slightly beyond the neck of the aneurysm. The tapered distal tip of the introducer is mated with the proximal hub of the delivery catheter, and the delivery wire is then advanced through the delivery catheter.
The CODMAN ENTERPRISE® stent device has a highly flexible, self-expanding closed cell design with a number of coils of radiopaque wire to serve as markers at each flared end of the device, similar to the stent illustrated in the published patent application by Jones et al., cited above. Manufacture of such markers is relatively time-consuming and expensive due to the small size of the stent and the need to wrap the radiopaque wire multiple times around struts on the stent, which is especially difficult within closed cells of the stent.
It is therefore desirable to increase radiopacity of an implant in a cost-effective manner while minimizing impacts to implant performance.